EVER SINCE BOOTSY COLLINS DID INDEED MAKE OUR FUNK THE P-Funk, bass players have gone ga-ga for envelope filters, those autoquackers beneath a great deal of uncut funk. While most of us know how they sound, many don’t quite get how they work. Here’s how:
1. Your bass’s signal enters the pedal and hits a buffer/booster stage to groom it for the envelope-follower circuitry. Generally, a pedal’s SENSITIVITY knob controls the behavior of this stage.
2. The signal is split and sent to the envelope follower and to a filter circuit.
3. The envelope follower creates a unipolar (all positive or negative, not both) signal in direct proportion to the amplitude of your bass’s signal. It’s not a perfect representation of the note-to-note changes in amplitude, but a reasonable approximation.
4. The output of the envelope follower is linked to the filter circuit. As the strength of this output changes, it has a corollary effect on the cutoff frequency of the filter applied to your bass’s signal.
5. For the classic quack sound, a lowpass filter is applied to the signal, and the cutoff moves up in proportion to how loud you play. Conversely, the cutoff can move down from the “resting” position, resulting in that dwoop sound, as opposed to the bwap sound.
6. The RESONANCE control on most pedals (it has different names depending on model) boosts the cut-off frequency of the sweeping filter, thus emphasizing the effect.